EP0627868B1

EP0627868B1 - Loudspeaker driver surrounding

Info

Publication number: EP0627868B1
Application number: EP94303190A
Authority: EP
Inventors: William P. Schreiber
Original assignee: Bose Corp
Current assignee: Bose Corp
Priority date: 1993-05-28
Filing date: 1994-05-03
Publication date: 2001-12-19
Anticipated expiration: 2014-05-03
Also published as: DE69429471D1; JPH07143593A; EP0627868A1; JP3396082B2; US5418337A; DE69429471T2

Description

The present invention relates in general to loudspeaker driver surrounding and more particularly concerns novel structure and techniques for improving loudspeaker driver performance with a novel surround shape which overlaps the diaphragm over much of its surface area and starts from EP-A-0 492 914.
An important goal of loudspeaker designers has been to provide a single loudspeaker driver characterized by substantially uniform acoustical energy output as a function of frequency over substantially the full frequency range. One prior art approach involved attaching a high compliance roll at the edge of a rigid cone body to improve the low frequency response. This approach not only does not correct irregularities in the high frequency response, but may even exacerbate midrange anomalies. Another approach uses driver cone materials of increased stiffness (modulus of elasticity) to increase high frequency output, but with increased irregularity in response.
It is an important object of the invention to provide a practically manufacturable driver characterized by a substantially uniform frequency response over a wide range of audio frequencies.
It is known that increasing the driver motor strength (BL)²/R_E, where B = motor gap magnetic field strength, L = length of voice coil wire in that gap, R_E = resistance of voice coil, increases the acoustical output of spectral components in the middle range of audio frequencies relative to the bass frequencies. Adding mass to the cone of a driver with high motor strength according to the invention reduces the midrange response to substantially the level of the bass response and extends the fundamental mass-compliance resonance of the system to lower bass frequencies. In embodiments of the invention, this mass is typically two to five times greater than that of a prior art driver. According to the another aspect of the invention, damping material is comolded with the flexible part of the surround from a material that has suitable flexibility and internal damping properties, this damping material being at the junction of the surround roll and cone body. According to still another feature of the invention, material with appropriate locations on the surface of the cone body to achieve smooth extended highfrequency power response.
In a specific form of the invention adding mass, providing an edge damping ring and distributing damping material over the surface of the cone in a single molded elastomeric surround which is laminated to the cone body over a substantial portion of the cone area produces a driver characterised by a substantially uniform power response as a function of frequency over a broad range of audio frequencies.
EP-A-0492914 and WO-A-92/01359 both disclose speaker assemblies with cones and surrounds each having cones formed from a stiff material and lower stiffness surround.
According to the invention, there is provided a loudspeaker diaphragm comprising,
stiff cone material filling substantially the entire area between an inner circle and an outer circle,
and a surround of stiffness significantly less than that of the stiff cone material characterised the surround further comprising:
vibratile material extending between the inner circle and the outer circle, the material having a thin compliant roll near the outer circle and, having an outer circular bead inside of and near the thin compliant roll,
and an inner ridge having both radial and tangential components extending between the inner circle and the outer circular bead,
the width of the outer circular bead and the inner ridge being significantly less than the diameter of the outer circle, wherein
the attachment area between the cone body and the surround covers a substantial portion of the cone body.
Numerous other features, objects and advantages of the invention will become apparent from the following detailed description when read in connection with the accompanying drawings in which:
FIG. 1 is a perspective view of a surround according to the invention;
FIG. 2 is a plan view of the surround of FIG. 1;
FIG. 3 is an elevational view of the diaphragm of FIG. 1;
FIG. 4 is a plan view of the diaphragm showing typical dimensions;
FIG. 5 is a sectional view through section 5-5 of FIG. 4;
FIG. 6 is an enlarged sectional fragmentary view along a radius of the surround illustrating structural features;
FIG. 7 is a plan view of a commercial embodiment of a surround according to the invention;
FIGS. 8 and 9 are sectional views through sections 8-8 and 9-9 of FIG. 7; and
FIG. 10 is a plan view of the surround of FIG. 7-9 attached to stiff cone material according to the invention.
With reference now to the drawings and more particularly FIGS. 1, 2 and 3 thereof, there are shown perspective, plan and elevational views, respectively, of an exemplary surround according to the invention. Surround 11 has at the outer edge a conventional semi-toroidal thin roll 13 in the region that is the typical compliant element of a cone assembly. There is also an inner circular bead 14. A generally clover-shaped ridge 15 extends between circular bead 14 and an inner diameter 16 corresponding substantially to the location of a dust cap. Ridge 15 comprises a number of contiguous segments each extending between inner diameter 16 and bead 14. The width of clover-shaped ridge 15 and bead 14 is significantly less than the diameter of surround 11, each width being of the order of the same magnitude.
The structural modifications to a conventional surround described above help smooth out the middle and upper frequency response of a driver with this surround. The effect of ridge 15 and bead 14 is to increase the mass and density factor along the indicated path to help dampen resonances in both radial and tangential vibrational modes which are inherent in all cones operating at frequencies where the wavelength of sound is in the cone material smaller than the diameter of the cone.
It is within the principles of the invention to add material to a conventional diaphragm in the indicated pattern, or in a similar axi-symmetric pattern with 4 or more lobes, which inner edge is generally in the shape of the periphery of a multi-petalled flower. Preferably, the surround is molded in the indicated pattern.
Referring to FIG. 4, there is shown a plan view of an exemplary embodiment with actual dimensions in millimeters indicated. Referring to FIG. 5, there is shown a sectional view through section 5-5 of FIG. 4 with dimensions indicated in millimeters. Referring to FIG. 6, there is shown an enlarged sectional view corresponding to detail B in FIG. 5 with actual dimensions indicated in millimeters.
One of the materials with suitable density and loss parameters for the surround is SBR rubber having Share A hardness of 50, rebound resilience of 38% per DIN 53-512, and density of 1.16 gr/cm.³ so that the weight of surround roll 13 is typically 1 gram, bead 14 is 4 grams and ridge 15 is 2 grams.
Referring to FIG. 7, there is shown a plan view with specific dimensions in millimeters and degrees of a commercial embodiment of the invention. Referring to FIG. 8, there is shown a sectional view through section 8-8 of FIG. 7. Referring to FIG. 9, there is shown a sectional view through section 9-9 of FIG. 7. Elements in FIGS. 7-9 which correspond to elements in FIGS. 4-6, respectively, are identified by the same reference numeral with an appended '.
The embodiment of FIGS. 7-9 are formed with rounded cutouts 15A for accommodating flexible leads from the loudspeaker driver voice coil dressed along the stiff cone portion for connection to leads connected to the rear side of the stiff cone portion to which the surround 11 is attached in the usual manner.
Referring to FIG. 10, there is shown a plan view of the surround of FIGS. 7-9 attached to the stiff cone body 21.
Appendix A is an embodiment of FIGS. 7-10.
The invention may be embodied in other forms. For example, weights may be attached to a diaphragm following the principles of the invention. Beads of silicon or other material may be attached to a conventional diaphragm.

Claims

A loudspeaker diaphragm comprising,

stiff cone material (21) filling substantially the entire area between an inner circle and an outer circle,

and a surround (11) of stiffness significantly less than that of the stiff cone material characterised by the surround (11) further comprising:

vibratile material extending between the inner circle and the outer circle, the material having a thin compliant roll (13) near the outer circle and, having an outer circular bead (14) inside of and near the thin compliant roll,

and an inner ridge (15) having both radial and tangential components extending between the inner circle and the outer circular bead (14),

the width of the outer circular bead (14) and the inner (15) ridge being significantly less than the diameter of the outer circle, wherein

the attachment area between the cone body and the surround covers a substantial portion of the cone body.
A loudspeaker diaphragm in accordance with claim 1, wherein the substantial portion is at least half the entire area.
A loudspeaker diaphragm in accordance with claim 1 or 2, wherein the width of the outer bead (14) is of the order of the width of the inner ridge (15).
A loudspeaker diaphragm in accordance with claim 1 or 2, wherein the inner ridge (15) defines a pattern symmetrical about the axis of the diaphragm.
A loudspeaker diaphragm in accordance with claim 4, wherein the inner edge of the pattern is substantially that of the periphery of a multi-petalled flower.
A loudspeaker diaphragm in accordance with claim 5, wherein the pattern has four leaves in spaced quadrature about the axis.
A loudspeaker diaphragm in accordance with claim 5, in which the pattern has eight leaves equally spaced about the axis.